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Annotation of OpenXM_contrib/gmp/mpz/cfdiv_q_2exp.c, Revision 1.1.1.1

1.1       ohara       1: /* mpz_cdiv_q_2exp, mpz_fdiv_q_2exp -- quotient from mpz divided by 2^n.
                      2:
                      3: Copyright 1991, 1993, 1994, 1996, 1998, 1999, 2001, 2002 Free Software
                      4: Foundation, Inc.
                      5:
                      6: This file is part of the GNU MP Library.
                      7:
                      8: The GNU MP Library is free software; you can redistribute it and/or modify
                      9: it under the terms of the GNU Lesser General Public License as published by
                     10: the Free Software Foundation; either version 2.1 of the License, or (at your
                     11: option) any later version.
                     12:
                     13: The GNU MP Library is distributed in the hope that it will be useful, but
                     14: WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
                     15: or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
                     16: License for more details.
                     17:
                     18: You should have received a copy of the GNU Lesser General Public License
                     19: along with the GNU MP Library; see the file COPYING.LIB.  If not, write to
                     20: the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
                     21: MA 02111-1307, USA. */
                     22:
                     23: #include "gmp.h"
                     24: #include "gmp-impl.h"
                     25:
                     26:
                     27: /* dir==1 for ceil, dir==-1 for floor */
                     28:
                     29: static void __gmpz_cfdiv_q_2exp _PROTO ((REGPARM_3_1 (mpz_ptr w, mpz_srcptr u, unsigned long cnt, int dir))) REGPARM_ATTR (1);
                     30: #define cfdiv_q_2exp(w,u,cnt,dir)  __gmpz_cfdiv_q_2exp (REGPARM_3_1 (w,u,cnt,dir))
                     31:
                     32: static void
                     33: cfdiv_q_2exp (mpz_ptr w, mpz_srcptr u, unsigned long cnt, int dir)
                     34: {
                     35:   mp_size_t  wsize, usize, abs_usize, limb_cnt, i;
                     36:   mp_srcptr  up;
                     37:   mp_ptr     wp;
                     38:   mp_limb_t  round, rmask;
                     39:
                     40:   usize = SIZ (u);
                     41:   abs_usize = ABS (usize);
                     42:   limb_cnt = cnt / GMP_NUMB_BITS;
                     43:   wsize = abs_usize - limb_cnt;
                     44:   if (wsize <= 0)
                     45:     {
                     46:       /* u < 2**cnt, so result 1, 0 or -1 according to rounding */
                     47:       PTR(w)[0] = 1;
                     48:       SIZ(w) = (usize == 0 || (usize ^ dir) < 0 ? 0 : dir);
                     49:       return;
                     50:     }
                     51:
                     52:   /* +1 limb to allow for mpn_add_1 below */
                     53:   MPZ_REALLOC (w, wsize+1);
                     54:
                     55:   /* Check for rounding if direction matches u sign.
                     56:      Set round if we're skipping non-zero limbs.  */
                     57:   up = PTR(u);
                     58:   round = 0;
                     59:   rmask = ((usize ^ dir) >= 0 ? MP_LIMB_T_MAX : 0);
                     60:   if (rmask != 0)
                     61:     for (i = 0; i < limb_cnt && round == 0; i++)
                     62:       round = up[i];
                     63:
                     64:   wp = PTR(w);
                     65:   cnt %= GMP_NUMB_BITS;
                     66:   if (cnt != 0)
                     67:     {
                     68:       round |= rmask & mpn_rshift (wp, up + limb_cnt, wsize, cnt);
                     69:       wsize -= (wp[wsize - 1] == 0);
                     70:     }
                     71:   else
                     72:     MPN_COPY_INCR (wp, up + limb_cnt, wsize);
                     73:
                     74:   if (round != 0)
                     75:     {
                     76:       if (wsize != 0)
                     77:        {
                     78:           mp_limb_t cy;
                     79:          cy = mpn_add_1 (wp, wp, wsize, CNST_LIMB(1));
                     80:          wp[wsize] = cy;
                     81:          wsize += cy;
                     82:        }
                     83:       else
                     84:        {
                     85:          /* We shifted something to zero.  */
                     86:          wp[0] = 1;
                     87:          wsize = 1;
                     88:        }
                     89:     }
                     90:   SIZ(w) = (usize >= 0 ? wsize : -wsize);
                     91: }
                     92:
                     93:
                     94: void
                     95: mpz_cdiv_q_2exp (mpz_ptr w, mpz_srcptr u, unsigned long cnt)
                     96: {
                     97:   cfdiv_q_2exp (w, u, cnt, 1);
                     98: }
                     99:
                    100: void
                    101: mpz_fdiv_q_2exp (mpz_ptr w, mpz_srcptr u, unsigned long cnt)
                    102: {
                    103:   cfdiv_q_2exp (w, u, cnt, -1);
                    104: }